1. Field Of The Invention
The present invention relates to computer system input devices such as a digitizers referred to as touchpads and more particularly to the systems and methods necessary to acquire signals from such input devices and to convert the acquired signals to digital codes that are transmitted to the computer system.
2. Description of Related Art
Touchpads are small digitizer based devices that are pen input devices to allow a person to write or draw upon the surface of the touchpad and have the signals and codes from a controller to be interpreted by a computer system. The touch pad digitizers may be of three types, capacitive, resistive and electromagnetic.
Referring to FIG. 1, the surface 12 of the touchpad becomes a "writing surface" for capturing the position of an pointed object 10 such as a finger, pen or stylus upon the touchpad. The touchpad signals are analog signals that will be captured by a touchpad interface circuit 28 and translated to digital codes that will be transferred to a computer system 32 on an interface 30. The interface 30 may be an industry standard serial interface, an industry standard parallel interface, or a custom interface requiring special adapter circuitry within the computer system 32 to accept the digital codes from the touchpad interface 28.
An example of a resistive touchpad is shown in FIG. 1. The resistive touchpad is made up of multiple layers of resistive films and protective layers. The protective hard coating 12 is the surface onto which the pointed object 10 is pressed upon during the writing and drawing. A first layer of resistive film 14 is attached to the protective hard coating 12 on the surface opposite the writing surface. This first layer of resistive film forms the Y-plane of the touchpad. Attached to the surface of the Y-plane resistive film 14 opposite the surface attached to the hard protective coating 12 is a second resistive film 16. This second resistive film 16 forms the X-plane of the touchpad. Finally attached to the side of the X-plane resistive film 16 is a supporting back layer 18. This back layer provides protection and mechanical support for the for the X-plane and Y-plane resistive films 14 and 16.
The touchpad interface 28 is connected through the touchpad interface lines 20, 22, 24, and 26. Each line will provide a stimulus such as a current or voltage to the periphery of the X-plane resistive film 16 and the Y-plane resistive film 14. As shown in FIG. 2, as the pointed object 10 is pressed 40 on the touchpad surface 12, the Y-plane resistive film 12 will deform and touch the X-plane resistive film 14. The X-plane resistive film can not deform because it is supported by the supporting back layer 18. This causes the Y-plane resistive film 14 and the X-plane resistive film 16 to come into contact with each other. This will cause a response in the form a change in voltage or current depending upon whether the stimulus from the touchpad interface 28 of FIG. 1 is a constant voltage or a constant current. If the stimulus from the touchpad interface 28 of FIG. 1 is a constant voltage the currents through the touchpad interface lines 20, 22, 24, and 26 will be modified according to the position of the pointed object 10 on the touchpad surface 12. However, if the stimulus from the touchpad interface 28 of FIG. 1 is a constant current the voltages between the touchpad interface lines 20, 22, 24, and 26 will be modified according the position of the pointed object 10 on the touchpad surface 12.
Referring back to FIG. 1, the touchpad interface 28 will have a set of analog to digital converters that will sense the change in the analog responses from the touchpad interface lines 20, 22, 24, and 26 and convert them to digital codes indicating the absolute position of the pointed object 10 upon the touchpad surface 12. The digital codes may be transmitted directly to the computer system across the interface 30 and translated to absolute coordinates within the computer system or the touchpad interface 28 may determine the absolute coordinates and transmit them directly to the computer system 32. For the computer system 32 to use the absolute coordinates generated by the touchpad interface 28 to control the movement of the cursor 36 upon the display screen 34, these absolute coordinates must be modified to codes that define the relative motion of the cursor 36. The relative motion will be the speed and direction of the cursor 36 as it is moved across the display screen 34. The modification from absolute coordinates to relative motion information must be done with in an internal mouse emulation program resident within the computer system 32.
A mouse is a point and click device that can be attached to a computer system to control the movement of a cursor on a display screen of the computer system. As described in "A Hardware and Software Resolution For A Pointing Device" AN569, in the Embedded Control Handbook, Microchip Technology Inc., 1994, "a standard motion translator for mice is the use of two slotted wheels, one each for horizontal and vertical direction. Also, there are two optical receivers per slotted wheel. As the slotted wheel turns, infrared beams of light are alternately transmitted and blocked, thereby sending a series of ones and zeros to optical transistor receivers. The two optical receivers are offset from each other such that the resulting signals are 90.degree. degrees out of phase. The phase difference results in two distinctly separate signals. The (mouse) controller interprets what direction the mouse is moving along either axis by the order is receives those two signals." The mouse controller counts the number of pulses per unit time and since the spacing of the slots and bars is uniform and equal in number, the relative velocity along each axis is calculated.
The direction and relative velocity are coded to set of mouse motion digital codes. These codes may be of several formats. Two representative mouse motion digital codes are shown in Table 1. The first is for the Microsoft Mouse from Microsoft Corp. and the second is for the PS/2 Mouse from International Business Machines (IBM).
TABLE 1 ______________________________________ Byte Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 ______________________________________ Microsoft Mouse Format 1 not used 1 L R V7 V6 H7 H6 2 not used 0 H4 H3 H2 HI HO 3 not used 0 V4 V3 V2 VI VO IBM PS/2 MOUSE FORMAT 1 Y OVR X OVR Y SIGN X SIGN RES RES SB PB FLOW FLOW 2 DELTA X MOTION 3 DELTA Y MOTION ______________________________________
For the Microsoft Mouse, Bit 5 of Byte 1 indicates if the left button of the mouse is depressed. Bit 4 of Byte 1 indicates if the right button of the mouse is depressed. Bits 3 and 2 of Byte 1 and bits 0 through 5 of the Byte 3 indicate the relative motion of the mouse in the vertical direction. Bits 1 and 0 of the Byte 1 and bits 0 through 5 of Byte 2 indicate the relative motion of the mouse in the horizontal direction. These codes form signed binary numbers. If the vertical signed binary number V0:V7 is positive the mouse is moving downward and if the vertical signed binary number V0:V7 is negative the mouse is moving upward. If the signed binary number H0:H7 is positive the mouse is moving toward the right and if the signed binary number H0:H7 is negative, the mouse if moving toward the left. The magnitudes of the horizontal H0:H7 and the vertical V0:V7 signed binary numbers indicate the relative velocity of the mouse movement.
For the IBM PS/2 mouse, Bit 0 of the first Byte indicates the Primary (in the Microsoft Mouse Left Mouse Button) Mouse button has been pressed. Bit 1 of the first Byte indicates the Secondary (in the Microsoft Mouse Right Mouse Button) Mouse button has been pressed. Bits 2 and 3 of the first Byte are reserved and not used. Bit 4 of the first Byte is an X direction sign bit, where if it is a 1, the X data (or horizontal) is negative and Bit 5 of the first Byte is a Y direction sign bit, where if it is a 1 the Y data (vertical) is negative. Bit 6 and Bit 7 of the first Byte are overflow bits for the X and Y data respectively, indicating that the mouse is traveling faster than the circuitry can reliably calculate its velocity. Byte 2 indicates the total movement (Delta X)of the mouse in the X direction since the last report of movement. Byte 3 indicates the total movement (Delta Y)of the mouse in the Y direction since the last report of movement.
If the touchpad is to emulate the mouse movements, when the cursor 36 is to moved across the display screen 34 for a relatively long distance, the pointed object 10 must be repeated lifted and placed back on the touchpad surface 12 repeatedly giving a "rowing" motion to get the cursor 36 to move the long distance. In traditional mouse operations, if the cursor 36 is to drag an object being displayed upon the display screen 34 a button on the mouse is depressed while the mouse is moved. The button can be held depressed while the mouse is moved in the rowing motion to drag the object across the display screen 34. This is difficult to accomplish on the touchpad. If the pointed object 10 is lifted from the touchpad, the touchpad interface 28 will not be able to communicate the "rowing" motion to indicate that the cursor 36 is to travel a long distance. Also, the touchpad interface 28 will not be able to communicate that there is an intention for the cursor 36 to drag the object on the display screen 34. Additional buttons must be added to the touchpad or special areas within the surface of the touchpad surface 12 in order for the touchpad interface 28 to communicate the desire for the cursor 36 to be moved long distances across the display screen 34 or that the cursor 36 is to drag objects upon the display screen 34.
Touchpads such as described in FIG. I have applications to mobile, portable, or lap top computing systems which are self contained and are powered by a battery power source. The amount of energy remaining in the a battery and the amount of energy consumed by the components of the computer system such as the touchpad and the touchpad interface are factors that must be continuously monitored and regulated to maximize the operation time of these mobile computer systems.
A class of mobile or portable computer systems are known as personal digital assistants. The personal digital assistant uses a touchpad as the primary human input interface. Handwriting must be interpreted to text and drawings to create commands and data to operate the personal digital assistant.
To interpret the hand writing accurately information regarding the pressure of the pen or stylus upon the touchpad and whether the pen is in contact with the touchpad to determine an end of a stroke for the formation of a character. Handwriting interpreting algorithms as currently applied, have only a series of recent history of the absolute coordinates of the location of the pointed object 10 of FIG. 1 upon the touchpad. From these coordinates the handwriting must be interpreted to commands and characters. If the pressure and stroke information is available handwriting interpretation could be more accurate.
U.S. Pat. No. 4,812,828 (Nishi, et al.) discloses a video display processor that is connected to a mouse or a light pen. The processor will place the pulse signals form a mouse to X and Y counters to create codes that represent the amount of movement of the mouse when in the mouse mode. The processor will clock the X and Y counters to create codes that represent the absolute coordinates of a light pen on a display screen, when in the light pen mode. And the processor will clock the X and Y counters until a collision signal, which is generated by associated circuitry, when the animation patterns of the video image are overlapped.
U.S. Pat. No. 5,260,697 (Barrett, et al.) discloses a digitizing tablet overlaying a display screen. The system allows for the simulation of computer input devices such as a mouse and keyboard by a pen upon the digitizing touch tablet. The simulations are accomplished through programs within an interface processor.
U.S. Pat. No. 5,327,161 (Logan, et al.) describes a method to emulate mouse input devices using a program resident within a computer system. A touchpad input device has a controller that generates a digital code that contains the absolute position of a pen or finger on the mouse pad. This requires a special interface that is unique to the touchpad circuitry. Additionally, this patent describes a method for the continuation of cursor movement when a pointed object is touching the touchpad and has been moved on the touchpad to a special border area. The pointed object must be stopped within the border for the continuous motion to be engaged. The direction of the scrolling may be made as a modification of the original direction and velocity of the pen prior to the transiting and stopping within the border area of the touchpad. This modification will be made as a change in the velocity of the movement of the cursor along an axis parallel to the edge of the touchpad adjacent to the border area where the pointed object is resting.
U.S. Pat. No. 5,376,946 (Mikan) describes a circuit using an EPROM to convert signals from a touch screen adhered to a computer display screen to digital codes of the industry standard computer input mouse protocols.
U.S. Pat. No. 5,420,943 (Mak) describes a universal input device for a computer which can be used as a point and click device to read bar codes, a bar code scanner, a mouse, a handwriting input device, or a text scanner. The device has a pen with a CCD array and pad with bar codes and a grids for accomplishing the mouse and bar code scanning functions.
U.S. Pat. No. 5,543,590 (Gillespie, et al.) describes a capacitive sensor system that can detect the location of a finger or stylus on a sensor matrix. The location is determined and translated as electrical signals for use in other circuitry such as a computer system to control a cursor upon a display screen. Further this patent discusses an "edge motion" detection feature that will allow a finger or stylus within a "outer zone" of the sensor matrix to move the cursor to move across a display screen for long distances and avoid the "rowing" motion.
U.S. Pat. No. 5,543,591 (Gillespie, et al.) discloses methods for recognizing tapping, pushing, hopping and zigzagging gestures upon a conductive sensor pad that can be interpreted into cursor control motions such as clicking, double clicking, and click and drag use with computer mouse devices. Further this patent also describes the "edge motion" feature as described in U.S. Pat. No. 5,543,590 (Gillespie, et al.).
U.S. Pat. No. 5,488,204 (Mead) shows a proximity sensor system that has a capacitive touchpad. The capacitance of the touchpad changes with the proximity of an object to the touchpad. As the capacitance changes a voltage changes which is converted to electrical signals representing the X and Y coordinates of the object on the touchpad. A conductive paint brush stylus is used to produce paint-like strokes on a display screen associated with the touchpad. The system also incorporates features that allow the stylus to emulate the actions of a computer mouse including an "edge motion" where a cursor can be moved over long distances without rowing or stroking the stylus.
U.S. Pat. No. 5,266,750 (Yatsuzuka) discloses a tablet input device and circuitry for providing stimulating voltages to the tablet input device and for sensing the response voltages from the tablet input device when the tablet input device is being pressed. The circuitry provides an OFF state wherein power to the tablet is minimized during a waiting period.
U.S. Pat. No. 5,568,409 (Neoh) assigned to the same assignee as the present invention, discloses a circuit for the implementation of the detection of a pointed object upon a touchpad and technique for the removal of power form the circuitry when the pointed object has not been detected upon the touchpad.
U.S. Pat. No. 5,287,121 (Louis, et al.) discloses a graphics input device where a stylus is used on a mechanism resembling a joy stick to provide horizontal graphics signals to a graphics processor and a feature within the mechanism to sense pressure upon the stylus to generate vertical graphics information.
U.S. Pat. No. 5,508,719 (Gervais) discusses a pressure activated pointing device for mobile or portable computing systems, where the output signals are proportional to the pressure on the pointing device.
The use of multiplexers within an analog-to-digital converter circuit is well known in the art. U.S. Pat. No. 5,446,371 (Eccleston, et al.), U.S. Pat. No. 5,150,120 (Yunus), U.S. Pat. No. 5,187,481 (Hiller), U.S. Pat. No. 4,656,585 (Stephenson), U.S. Pat. No. 4,616,325 (Heckenbach, et al.), and U.S. Pat. No. 4,196,358 (Conover, et al.) describe various applications of analog and digital multiplexing circuits for use within analog-to-digital converters.